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Date: Thu, 6 Feb 2020 02:11:56 -0800
Subject: Re: [EE] 78L05 (SO8) overshoot on removal of over-current event?
Thread-Topic: [EE] 78L05 (SO8) overshoot on removal of over-current event?
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Quoting RussellMc <apptechnz@gmail.com>:

> On Thu, 6 Feb 2020 at 06:50, David Van Horn <
> david.vanhorn@backcountryaccess.com> wrote:
>
>> I've not seen this exactly, but I have seen a lot of problems with the L
>> version being defective in various ways.  I generally wouldn't trust the=
m.
>>
>> They (and actually most PNP based regulators) can be damaged by the inpu=
t
>> being shorted to ground, if the output capacitor is large.  This is not
>> well documented, you might have to go back to Motorola data sheets from =
the
>> 1980's to find it documented, but the output stages are still much the
>> same.   There are more modern parts that are immune.
>>
>> Normal method  to protect against this is to place a reverse biased diod=
e
> across the regulator so that the output capacitor will discharge via the
> diode if the input is shorted.

Hi, Russell:-

The old NS datasheets say "generally" no diode is required for 10uF or =20
less output capacitor on the 7805. That may be a relic of the =20
electrolytic capacitors of old, which would have enough ESR (1-2 ohms =20
maybe) to limit the current. Maybe a modern 10uF ceramic cap can ruin =20
the regulator given a
direct short.

> Worst case a power off event may qualify if there is a heavy load on the
> input side from loads.
>
> I recall, but now not why in detail, that many decades ago we decided tha=
t
> the 78Lxx regulators were not worth using compared to the 'full spec' one=
s.

I picked 78Mxx many years ago for a whole series of applications where a
78L0x would function because they are superior electrically in just =20
about every respect, in particular the temperature coefficient, line =20
regulation, load regulation and PSRR are better. Less temperature rise =20
with a TO-252 on a
bit of copper or a TO-220 too.

Best regards,
Spehro Pefhany


>
>        Russell
> --
> http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive
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